Method and apparatus for providing optimal transmission and reception beams in beamforming system

ABSTRACT

A method of providing an optimal transmission or reception (Tx/Rx) beam in a beamforming system. The method includes receiving a reference signal and selecting an optimal Tx/Rx beam that guarantees an optimal channel environment based on the received reference signal determining a possibility of occurrence of a Tx/Rx beam mismatch between the selected optimal Tx/Rx beam and a Tx/Rx beam used for transmitting information on the selected optimal Tx/Rx beam; and when there is the possibility of the occurrence of the Tx/Rx beam mismatch, performing at least one of widening a beam width of the Tx/Rx beam, increasing a number of Tx/Rx beams, reducing a period of a beam selection operation for selecting the optimal Tx/Rx beam, and reducing a transmission period of the reference signal. Other embodiments including a beamforming system are also disclosed.

CROSS-REFERENCE TO RELATED APPLICATION AND CLAIM OF PRIORITY

The present application is a divisional of U.S. application Ser. No.14/266,555 filed on Apr. 30, 2014 and claims priority under 35 U.S.C.§119(a) to Korean Application Serial No. 10-2013-0048148, which wasfiled in the Korean Intellectual Property Office on Apr. 30, 2013, theentire content of which are hereby incorporated by reference.

TECHNICAL FIELD

The present disclosure relates to a method and an apparatus forproviding optimal transmission and reception beams in a beamformingcommunication system for supporting a beamforming scheme.

BACKGROUND

With the use of terminals, such as a smart phone and the like, anaverage amount of data used by mobile communication users hasexponentially increased and users' demands for a higher datatransmission rate also have continuously increased. A method ofproviding a generally high data transmission rate includes a method ofproviding a communication service using a wider frequency band and amethod of increasing frequency usage efficiency. However, it is verydifficult to provide a higher average data transmission rate through themethod of increasing the frequency usage efficiency. It is becausecurrent communication technologies have already provided frequency usageefficiency close to a theoretical limit and further increasing thefrequency usage efficiency through technology improvement is difficult.

Accordingly, providing the communication service through a widerfrequency band is a realizable method of increasing the datatransmission rate. At this time, it is required to consider an availablefrequency band. In view of the current frequency distribution policy, aband in which broadband communication of 1 GHz or more is possible islimited and a practically selectable frequency band is only themillimeter wave band of 30 GHz or more. In such a high frequency band, abase station using power equal to power used in a conventional cellularsystem has significantly reduced coverage in which a service isprovided. In order to solve the above problem, a beamforming scheme thatconcentrates transmission or reception power in a narrow space toincrease transmission or reception efficiency of an antenna is widelyused.

SUMMARY

To address the above-discussed deficiencies, it is a primary object toprovide a method and an apparatus for providing optimal Tx and Rx beamsto each of a BS and a UE by solving a Tx/Rx beam mismatch problem in abeamforming system.

Further, the present disclosure provides a method and an apparatus fordetermining a possibility of the generation of the Tx/Rx beam mismatchin the beamforming system based on reciprocity between UL and DL andperforming a proactive protection operation to prevent the generation ofthe Tx/Rx beam mismatch in advance.

In addition, the present disclosure provides a method and an apparatusfor determining the generation of the Tx/Rx beam mismatch in thebeamforming system and performing a reactive compensation operationbased on reciprocity between UL and DL.

In accordance with an aspect of the present disclosure, a method ofproviding an optimal transmission or reception (Tx/Rx) beam in abeamforming system is provided. The method includes receiving areference signal and selecting an optimal Tx/Rx beam that guarantees anoptimal channel environment based on the received reference signal,determining a possibility of a generation of a Tx/Rx beam mismatchbetween the selected optimal Tx/Rx beam and a Tx/Rx beam used fortransmitting information on the selected optimal Tx/Rx beam, and whenthere is the possibility of the generation of the Tx/Rx beam mismatch,performing at least one of an operation of widening a beam width of theTx/Rx beam, an operation of increasing a number of Tx/Rx beams, anoperation of reducing a period of a beam selection operation forselecting the optimal Tx/Rx beam, and an operation of reducing atransmission period of the reference signal.

In accordance with another aspect of the present disclosure, a method ofproviding an optimal transmission/reception (Tx/Rx) beam in abeamforming system is provided. The method includes receiving areference signal and a control signal and selecting an optimal Tx/Rxbeam that guarantees an optimal channel environment based on thereceived reference signal and control signal, determining whether aTx/Rx beam mismatch occurs between the selected optimal Tx/Rx beam and aTx/Rx beam used for transmitting information on the selected optimalTx/Rx beam, when the Tx/Rx beam mismatch occurs, selecting a new Tx/Rxbeam based on pre-received Tx/Rx beam information; and transmittingcompensation information including at least one of information relatedto a User Equipment (UE) and information on the optimal Tx/Rx beam byusing the new Tx/Rx beam.

In accordance with another aspect of the present disclosure, anapparatus for providing an optimal transmission/reception (Tx/Rx) beamin a beamforming system is provided. The apparatus includes: a receiverthat receives a reference signal, and a controller that selects anoptimal Tx/Rx beam that guarantees an optimal channel environment basedon the received reference signal, determines a possibility of ageneration of a Tx/Rx beam mismatch between the selected optimal Tx/Rxbeam and a Tx/Rx beam used for transmitting information on the selectedoptimal Tx/Rx beam, and, when there is the possibility of the generationof the Tx/Rx beam mismatch, performs at least one of an operation ofwidening a beam width of the Tx/Rx beam, an operation of increasing anumber of Tx/Rx beams, an operation of reducing a period of a beamselection operation for selecting the optimal Tx/Rx beam, and anoperation of reducing a transmission period of the reference signal.

In accordance with another aspect of the present disclosure, anapparatus for providing an optimal transmission/reception (Tx/Rx) beamin a beamforming system is provided. The apparatus includes a receiverconfigured to receive a reference signal and a control signal, acontroller configured to select an optimal Tx/Rx beam that guarantees anoptimal channel environment based on the received reference signal andcontrol signal, determine whether a Tx/Rx beam mismatch occurs betweenthe selected optimal Tx/Rx beam and a Tx/Rx beam used for transmittinginformation on the selected optimal Tx/Rx beam, and select, when theTx/Rx beam mismatch occurs, a new Tx/Rx beam based on pre-received Tx/Rxbeam information, and a transmitter configured to transmit compensationinformation including at least one of information related to a UserEquipment (UE) and information on the optimal Tx/Rx beam by using thenew Tx/Rx beam.

According to the present disclosure, it is possible to prevent theoccurrence of the Tx/Rx beam mismatch in advance by performing aproactive protection operation through determining beforehand apossibility of the generation of the UL and DL Tx/Rx beam mismatch.Further, even when the Tx/Rx beam mismatch occurs, an optimal Tx/Rx beamcan be provided to each of the BS and the UE by performing a reactivecompensation operation for each of the UL and the DL.

Before undertaking the DETAILED DESCRIPTION below, it may beadvantageous to set forth definitions of certain words and phrases usedthroughout this patent document: the terms “include” and “comprise,” aswell as derivatives thereof, mean inclusion without limitation; the term“or,” is inclusive, meaning and/or; the phrases “associated with” and“associated therewith,” as well as derivatives thereof, may mean toinclude, be included within, interconnect with, contain, be containedwithin, connect to or with, couple to or with, be communicable with,cooperate with, interleave, juxtapose, be proximate to, be bound to orwith, have, have a property of, or the like; and the term “controller”means any device, system or part thereof that controls at least oneoperation, such a device may be implemented in hardware, firmware orsoftware, or some combination of at least two of the same. It should benoted that the functionality associated with any particular controllermay be centralized or distributed, whether locally or remotely.Definitions for certain words and phrases are provided throughout thispatent document, those of ordinary skill in the art should understandthat in many, if not most instances, such definitions apply to prior, aswell as future uses of such defined words and phrases.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure and itsadvantages, reference is now made to the following description taken inconjunction with the accompanying drawings, in which like referencenumerals represent like parts:

FIG. 1 illustrates an example in which a Base Station (BS) and a UserEquipment (UE) select an optimal transmission/reception (Tx/Rx) beam ina beamforming system;

FIG. 2 illustrates an example in which a BS transmits/receives a signalthrough a beam having a specific beam width in the beamforming system;

FIG. 3 illustrates an example of a Tx beam region in which a BS cantransmit a Tx beam to downlink and an Rx beam region in which the BS canreceive the Tx beam;

FIG. 4 illustrates a process of selecting a beam in the downlink/uplinkand a process of exchanging information on the selected beam in abeamforming system;

FIG. 5A illustrates an example where a Tx/Rx beam mismatch occurs by anincrease in a movement speed of a UE and a rapid change in a channelenvironment in the beamforming system;

FIG. 5B illustrates an example in which a Tx/Rx beam mismatch occurs dueto an appearance of obstacles in the beamforming system;

FIG. 6 illustrates an example of a frame structure used for transmittingor receiving a signal in the beamforming system according to anembodiment of the present disclosure;

FIG. 7 is a flowchart illustrating an example in which a BS determines apossibility of the generation of the Tx/Rx beam mismatch in thebeamforming system and performs a proactive protection operationaccording to an embodiment of the present disclosure;

FIG. 8 is a flowchart illustrating an example in which a BS determines apossibility of the generation of the Tx/Rx beam mismatch in thebeamforming system and performs a reactive compensation operationaccording to an embodiment of the present disclosure;

FIG. 9 is a flowchart illustrating an example in which a BS performs areactive compensation operation in the beamforming system according toan embodiment of the present disclosure;

FIG. 10 is a flowchart illustrating an example in which a BS performs areactive compensation operation in the beamforming system according toanother embodiment of the present disclosure;

FIG. 11 is a flowchart illustrating an example in which a UE determinesa possibility of the generation of the Tx/Rx beam mismatch in thebeamforming system and performs a proactive protection operationaccording to an embodiment of the present disclosure;

FIG. 12 is a flowchart illustrating an example in which a UE determinesa possibility of the generation of the Tx/Rx beam mismatch in thebeamforming system and performs a reactive compensation operationaccording to an embodiment of the present disclosure;

FIG. 13 is a flowchart illustrating an example in which a UE performs areactive compensation operation in the beamforming system according toan embodiment of the present disclosure;

FIG. 14 is a flowchart illustrating a process in which a UE receivessystem information in the beamforming system according to an embodimentof the present disclosure;

FIG. 15 is a block diagram illustrating a structure of a BS apparatusthat provides an optimal Tx/Rx beam to a UE by solving a Tx/Rx beammismatch problem in the beamforming system according to an embodiment ofthe present disclosure; and

FIG. 16 is a block diagram illustrating a structure of a UE apparatusthat provides an optimal Tx/Rx beam to a BS by solving the Tx/Rx beammismatch problem in the beamforming system according to an embodiment ofthe present disclosure.

DETAILED DESCRIPTION

FIGS. 6 through 16, discussed below, and the various embodiments used todescribe the principles of the present disclosure in this patentdocument are by way of illustration only and should not be construed inany way to limit the scope of the disclosure. Those skilled in the artwill understand that the principles of the present disclosure may beimplemented in any suitably arranged telecommunication technologies.Hereinafter, exemplary embodiments of the present disclosure will bedescribed in detail with reference to the accompanying drawings.Further, in the following description of the present disclosure, adetailed description of known functions and configurations incorporatedherein will be omitted when it may make the subject matter of thepresent disclosure rather unclear. The terms which will be describedbelow are terms defined in consideration of the functions in the presentdisclosure, and may be different according to users, intentions of theusers, or customs. Accordingly, the terms should be defined based on thecontents over the whole present specification.

FIG. 1 illustrates an example in which a Base Station (BS) and a UserEquipment (UE) select an optimal transmission or reception (Tx/Rx) beamin a beamforming system.

Referring to FIG. 1, it is assumed that a communication region 120includes a first cell 100, a second cell 102, and a third cell 104, anda BS 110 transmits or receives data to or from a UE 130 by using aplurality of array antennas, that is, array 0 and array 1 in each cell.At this time, the BS 110 can transmit data while changing a direction ofa downlink Transmission (Tx) beam and the UE 130 can receive data whilechanging a direction of a downlink Reception (Rx) beam.

In a beamforming system in which communication is performed using abeamforming scheme, the BS 110 and the UE 130 have a characteristic ofselecting a Tx beam direction and an Rx beam direction that guarantee anoptimal channel environment among various Tx beam directions and Rx beamdirections to transmit or receive data. Such a characteristic isidentically applied to an uplink channel in which the UE 130 transmitsdata to the BS 110 as well as a downlink channel in which the BS 110transmits data to the UE 130.

For example, when it is assumed that a number of Tx beam directionswhich can be used by the BS 110 is N and a number of Rx beam directionswhich can be used by the UE 130 is M, a process of selecting an optimaldownlink Tx/Rx beam direction (or beam) that guarantees an optimalchannel environment is described below.

The BS 110 transmits prearranged signals, for example, reference signalsby M times or more in N directions. The UE 130 receives the referencesignals transmitted in the N directions by using Rx beams of Mdirections. In such a process, the BS 110 is required to transmitparticular reference signals by at least N×M times and the UE 130 isrequired to receive the reference signals by N×M times and measure areception strength of each of the received signals. Thereafter, each ofthe BS 110 and the UE 130 selects a Tx/Rx beam direction correspondingto a strongest measured value among the N×M measured values as anoptimal Tx/Rx beam direction.

Particularly, in the above described process, a process in which the BS110 transmits the signal in all available beam directions by one time ormore and the UE 130 receives the signal in all available beam directionsis referred to as a “beam sweeping process” and a process in which theUE 130 selects the optimal Tx/Rx beam direction is referred to as a“beam selection process”. Further, although the process of selecting theoptimal downlink Tx/Rx beam has been described herein, the Tx/Rx beamselecting process can be equally applied to the uplink. That is, theoptimal uplink Tx/Rx beam is also selected by the same process as theaforementioned beam selecting process.

FIG. 2 illustrates an example in which the BS transmits/receives asignal through a beam having a specific beam width in a beamformingsystem.

Referring to FIG. 2, it is assumed that a BS 210 is installed in aposition of a particular height 201 and a beam transmitted from the BShas a predetermined beam width 202. The beam width of the BS can bedefined with respect to each of an elevation angle and an azimuth andFIG. 2 illustrates that the BS 210 transmits/receives a signal through abeam corresponding to a particular elevation angle 203.

FIG. 3 illustrates an example of a Tx beam region in which the BS cantransmit a Tx beam to the downlink and an Rx beam region in which the BScan receive the Tx beam in a beamforming system.

Referring to FIG. 3, it is assumed that a BS 310 is installed in aposition of a height of 35 m and the BS 310 transmits a Tx beam having abeam width of 5 degrees with respect to each of the elevation angle andthe azimuth within a sector having an angle of 30 degrees and a coverageof 200 m in the same way as illustrated in FIG. 2.

That is, an example of FIG. 3 illustrates a case where a sector havingan angle of 30 degrees and a coverage of 200 m is configured using 96 Txbeams having a beam width of 5 degrees with respect to each of theelevation angle and the azimuth. When there is no obstacle, the Tx beamstransmitted by the BS 310 are spread and transmitted with a fan shape.However, in the example of FIG. 3, it is assumed that each of the Txbeams reaches the ground with a rectangular shape for the convenience ofdescription.

The shown rectangles are shown by 96 regions and indicates the groundwhich Tx beams having a particular azimuth and elevation angle reach.The 96 Tx beams are transmitted to a region farther from the BS 310 asthe elevation angle is larger and a Tx beam transmitted to a regionfarther from the BS 310 is received in a wider region. A ratio %belonging to each of the shown rectangles indicates a ratio of an areawhich a reception region receiving the Tx beam transmitted to thecorresponding position occupies in a total number of 96 regions. Asillustrated in FIG. 3, a Tx beam transmitted to a boundary region of theBS 310 is received in a very wide region in comparison with a Tx beamtransmitted to a center region of the BS 310 even though the Tx beamshave the same elevation angle and azimuth. In the example of FIG. 3, thereception region of the Tx beam transmitted to the boundary region andthe reception region of the Tx beam transmitted to the center region hasan area difference of a maximum of 480 times.

In the beam forming system, the UE has a difficulty in forming a numberof transmission/reception beams having a narrow beam width generallylike the base station, due to limitations on a physical space,capability, price and the like. The example of FIG. 3 assumes a casewhere a UE 330 forms four Rx beams (beam 1, beam 2, beam 3, and beam 4)and receives the Tx beam of the BS 310 by using one of the formed fourRx beams. In this case, a beam width according to an azimuth of each ofthe Rx beams has approximately about 90 degrees.

As illustrated in the example of FIG. 3, when a Tx beam having a narrowbeam width, that is, a small elevation angle and a small azimuth isused, a large number of Tx beam regions and Rx beam regions exist withinthe BS coverage. Particularly, when a downlink synchronization channelsignal and broadcast control channel signals transmitted in a beamsweeping scheme are transmitted using the Tx beam having the narrow beamwidth, that is, a narrow Tx beam as illustrated in the example of FIG.3, the BS 310 should transmit the signal repeatedly a minimum of 96times in all available transmission beam directions within the BScoverage and each of the beam directions is used once or more. Asdescribed above, a number of times by which the downlink synchronizationsignal and the broadcast control channel signals are transmitted in thebeam sweeping scheme is proportional to a number of Tx beams transmittedwithin the BS coverage. Accordingly, in order to reduce transmissionoverheads due to the downlink synchronization signal and the broadcastcontrol channel signals, a method of supporting communication of a BScoverage region by a smaller number of Tx beams is required. Further, tothis end, it is advantageous to use a Tx beam having a wide beam width,that is, a wide Tx beam rather than a narrow Tx beam.

However, in general, as a beam width becomes wider, a beamforming effectdecreases. Further, when the beam width becomes narrower to increase thebeamforming effect, a number of Tx beams required for supporting the BScoverage increases, so that the transmission overheads due to thedownlink synchronization signal and the broadcast control channelsignals increase. As described above, the beamforming effect and thetransmission overheads due to the downlink synchronization signal andthe broadcast control channel signals have a trade off relationshiptherebetween.

In order to effectively solve the above problem, a method ofdiversifying a Tx beam width used for transmitting the broadcast channelsignal and a Tx beam width used for transmitting user data is generallyused. For example, in a sector having an angle of 60 degrees, the BStransmits the broadcast channel signal by using a Tx beam having a beamwidth of 30 degrees and transmits the user data by using a Tx beamhaving a beam width of 10 degrees. Hereinafter, the beam having the widebeam width is defined as a “wide beam” or a “coarse beam” and the beamhaving the narrow beam width is defined as a “narrow beam” or a “finebeam”.

The UE selects a beam by using a downlink reference signal transmittedto the wide beam or the narrow beam. Further, in order to receive datafrom the BS, the UE reports information on one or more downlink Tx beamsselected during the beam selecting process and a reception capability ofa downlink radio channel measured in the process to the BS. At thistime, since the beamforming should be also applied to the uplink, the BSand the UE are required to separately perform a beam selecting processfor the uplink.

The example of FIG. 3 has described the downlink beamforming as anexample. However, it goes without saying that all examples of FIG. 3 canbe equally applied to the uplink.

FIG. 4 illustrates a process of selecting a beam in downlink or uplinkand a process of exchanging information on the selected beam in thebeamforming system.

Referring to FIG. 4, a downlink beam selecting process 420 and an uplinkbeam selecting process 430 are distinguished from each other.

In the downlink beam selecting process 420, a BS 400 transmits DownLink(DL) reference signals through a beam sweeping process and a UE 410receives the DL reference signals through a beam sweeping process instep 401. The UE 410 selects an optimal DL Tx beam and Rx beam (or apair of optimal Tx and Rx beams) based on the received reference signalsand reports information on the selected pair of optimal Tx and Rx beams,for example, a beam index and Channel State Information (CSI) indicatinga reception capability of a radio channel to the BS 400 in step 402.

In the uplink beam selecting process 430, the UE 410 transmits UpLink(UL) reference signals through a beam sweeping process and the BS 400receives the UL reference signals through a beam sweeping process instep 403. The BS 400 selects a pair of optimal UL Tx and Rx beams basedon the received reference signals and reports an index of the selectedpair of optimal Tx and Rx beams to the UE 410 through a control channel,for example, a Physical Downlink Control CHannel (PDCCH) in step 404.

That is, a result of the beam selection for the DL by the UE 410, thatis, information on the pair of optimal DL Tx and Rx beams is transmittedto the BS 400 through the UL and a result of the beam selection for theUL by the BS 400, that is, information on the optimal UL Tx and RX beamsis transmitted to the UE 410 through the DL.

Meanwhile, when the UE 410 initially establishes communication with theBS 400, the UE 410 is required to simultaneously perform the beamselection processes for both the DL and the UL. In this case, althoughthe UE 410 should transmit the beam selection result for the DL to theBS 400 through UL, the beam selecting process for the UL has not beencompleted, so that the UE 410 has a difficulty in transmitting the beamselection result to the BS 400. Similarly, although the BS 400 shouldtransmit the beam selection result for the UL to the UE 410 through theDL, the beam selecting process for the DL has not been completed, sothat the BS 400 has a difficulty in transmitting the beam selectionresult to the UE 410. In order to solve the above problem, it can beassumed that information to be transmitted is transmitted using allavailable pairs of Tx and Rx beams in the initial establishment of thecommunication in steps 402 and 404.

Further, the illustrated beam selecting process is normally performedfor a UE having general mobility. However, due to a very fast speed ofthe UE or sudden appearance of obstacles, capabilities of used Tx and Rxbeams can simultaneously deteriorate or the Tx and Rx beams can besimultaneously blocked in steps 402 and 404. In this case, a mismatchbetween the optimal Tx and Rx beams determined in steps 401 and 403 andthe Tx and Rx beams used for actual transmission or reception in steps402 and 404 occurs. Further, due to the Tx/Rx beam mismatch, theinformation on the optimal Tx and Rx beams determined in steps 401 and403 cannot be transmitted to the BS 400 and the UE 410.

FIG. 5A illustrates an example where a Tx/Rx beam mismatch occurs by anincrease in a movement speed of the UE and a rapid change in a channelenvironment in the beamforming system.

Referring to FIG. 5A, it is assumed that a UE, located at a position501, receives a DL signal by using BS_Tx beam 1 and UE_Rx beam 1corresponding to a pair of optimal DL Tx and Rx beams and a BS 503receives a UL signal by using UE_Tx beam 1 and BS_Rx beam 1corresponding to a pair of optimal UL Tx and Rx beams.

When the UE located at the position 501 moves to a position 502 at veryfast speed or a channel environment around the UE is rapidly changed,the pair of optimal DL Tx and Rx beams (BS_Tx beam 1 and UE_Rx beam 1)are not the optimal Tx and Rx beams any more. At this time, the UElocated at the position 502 can select a new pair of optimal DL Tx andRx beams, for example, BS_Tx beam 25 and UE_Rx beam 4 by re-performingthe DL Tx/Rx beam selecting process. However, when information on thenew pair of optimal DL Tx and Rx beams is transmitted through the pairof optimal UL Tx and Rx beams (UE_Tx beam 1 and BS_Rx beam 1) used inthe position 501, the BS 503 may not receive the information on the newpair of optimal DL Tx and Rx beams.

Similarly, the BS 503 can select a new pair of optimal UL Tx and RXbeams, for example, UE_Tx beam 4 and BS_Rx beam 25 for the UE located atthe position 502. However, when information on the new pair of optimalUL Tx and Rx beams is transmitted through the pair of optimal DL Tx andRx beams (BS_Tx beam 1 and UE_Rx beam 1) used in the position 501, theUE located at the position 502 may also not receive the information onthe new pair of optimal DL Tx and Rx beams.

FIG. 5B illustrates an example in which a Tx/Rx beam mismatch occurs dueto an appearance of obstacles in the beamforming system.

Referring to FIG. 5B, it is assumed that a UE located at a position 505receives a DL signal by using BS_Tx beam 25 and UE_Rx beam 1corresponding to a pair of optimal DL Tx and Rx beams and a BS 506receives a UL signal by using UE_Tx beam 1 and BS_Rx beam 25corresponding to a pair of optimal UL Tx and Rx beams.

When obstacles 504 interrupt communication between the UE located at theposition 505 and the BS 506, the pair of optimal DL Tx and Rx beams(BS_Tx beam 25 and UE_Rx beam 1) are not the optimal Tx and Rx beams anymore. At this time, the UE located at the position 505 can select a newpair of optimal DL Tx and Rx beams, for example, BS_Tx beam 1 and UE_Rxbeam 4 by re-performing the DL Tx/Rx beam selecting process. However,when information on the new pair of optimal DL Tx and Rx beams istransmitted through the pair of optimal UL Tx and Rx beams (UE_Tx beam 1and BS_Rx beam 25), the BS 506 may not receive the information on thenew pair of optimal DL Tx and Rx beams.

Similarly, the BS 506 can select a new pair of optimal UL Tx and RXbeams, for example, UE_Tx beam 4 and BS_Rx beam 1 for the UE located atthe position 505. However, when information on the new pair of optimalUL Tx and Rx beams is transmitted through the pair of optimal DL Tx andRx beams (BS_Tx beam 25 and UE_Rx beam 1), the UE may also not receivethe information on the new pair of optimal DL Tx and Rx beams.

As described above, when the Tx and Rx beam mismatch problem occurs,each of the UE and the BS can select a new pair of optimal Tx and Rxbeams for the DL and the UL. However, in order to exchange informationon the new pair of optimal Tx and Rx beams between the UE and BS, thenew pair of optimal Tx and Rx beams should be repeatedly transmittedusing all available pairs of Tx and Rx beams through the beam sweepingprocess. Further, the above problem causes an unnecessary delay in theprocess of exchanging the new pair of optimal Tx and Rx beams and thushinders service continuity.

FIG. 6 illustrates an example of a frame structure used fortransmitting/receiving a signal in a beamforming system according to anembodiment of the present disclosure.

Referring to FIG. 6, a frame 600 has a length of 5 ms and includes fivesub-frames. The each sub-frame having a length of 1 ms, for example, asub-frame 610 includes a DL sub-frame 620 used if the BS transmits a DLsignal to the UE and a UL sub-frame 630 used if the UE transmits asignal to the BS.

The DL sub-frame 620 includes a scheduling region 602, a SynchronousCHannel (SCH)/Broadcasting CHannel (BCH) region 604, and a referencesignal region 606. Scheduling information is transmitted in thescheduling region 602, an SCH signal and a BCH signal are transmitted inthe SCH/BCH region 604, and a reference signal is transmitted in thereference signal region 606. Particularly, the SCH/BCH region 604 isincluded only in first sub-frame 610 among the sub-frames included inthe frame 600.

Hereinafter, an embodiment of the present disclosure will be describedin more detail with reference to FIGS. 7 to 14. Prior to the descriptionof the embodiment of the present disclosure, a method of providing anoptimal Tx/Rx beam to each of the BS and the UE provided by the presentdisclosure will be briefly described below. The method of providing theoptimal Tx/Rx beam provided by the present disclosure will be describedby two methods including a proactive protection method and a reactivecompensation method.

(1) Proactive Protection Method

Each of the BS and the UE determines a possibility of the occurrence ofthe mismatch between an optimal Tx/Rx beam selected based on receivedreference signals and a Tx/Rx beam actually used for transmittinginformation on the selected optimal Tx/Rx beam. When the BS and the UEdetermine that there is the possibility of the occurrence of the Tx/Rxbeam mismatch, the BS and the UE perform a proactive protectionoperation for each of UL and DL. The operation in which each of the BSand the UE determines the possibility of the occurrence of the Tx/Rxbeam mismatch will be described later in more detail with reference toFIGS. 7 and 11.

The proactive protection operation refers to an operation which each ofthe BS and the UE performs to prevent the occurrence of the Tx/Rx beammismatch in advance. That is, the proactive protection operation can beperformed using at least one of a method of increasing a diversityeffect by widening a width of a Tx/Rx beam and increasing a number ofTx/Rx beams, a method of reducing a period of a Tx/Rx beam selectingoperation for selecting an optimal Tx/Rx beam, and a method of reducinga transmission period of a reference signal.

(2) Reactive Compensation Method

Each of the BS and the UE determines whether the mismatch occurs betweenan optimal Tx/Rx beam selected based on received reference signals and aTx/Rx beam actually used for transmitting information on the selectedoptimal Tx/Rx beam. If the Tx/Rx beam mismatch occurs, the BS and the UEperform a reactive compensation operation for each of UL and DL. Theoperation in which each of the BS and the UE determines whether theTx/Rx beam mismatch occurs will be described in more detail withreference to FIGS. 8 to 10 and FIGS. 12 to 14 described later.

The reactive compensation operation refers to an operation in which eachof the BS and the UE performs to compensate the Tx/Rx beam mismatch whenthe Tx/Rx beam mismatch occurs.

That is, If the Tx/Rx beam mismatch occurs, based on an assumption ofthe reciprocity between the UL and the DL, the BS selects a new DL Tx/Rxbeam based on pre-received UL Tx/Rx beam information and transmitscompensation information including an identifier of the UE and optimalUL Tx/Rx beam information to the UE by using the selected DL Tx/Rx beam.Further, the BS can repeatedly perform an operation of transmitting thecompensation information to the UE until the BS receives a responsemessage of the compensation information from the UE or transmits thecompensation information in all available Tx beam directions.

Alternatively, the BS can configure and transmit the compensationinformation including the identifier of the UE and the optimal UL Tx/Rxbeam information in primary and secondary BCH regions of a DL sub-frame.

If the Tx/Rx beam mismatch occurs, based on an assumption of thereciprocity between the UL and the DL, the UE selects a new UL Tx/Rxbeam based on received DL Tx/Rx beam information and transmitscompensation information including an identifier of the UE and optimalDL Tx/Rx beam information to the BS by using the selected UL Tx/Rx beam.Further, the UE can repeatedly perform an operation of transmitting thecompensation information to the BS until the UE receives a responsemessage of the compensation information from the BS or transmits thecompensation information in all available Tx beam directions.

FIG. 7 is a flowchart illustrating an example in which the BS determinesa possibility of the occurrence of the Tx/Rx beam mismatch and performsthe proactive protection operation in the beamforming system accordingto an embodiment of the present disclosure.

Referring to FIG. 7, it is assumed that the BS determines thepossibility of the occurrence of the Tx/Rx beam mismatch in particularsub-frame n.

The BS receives a UL reference signal from the UE in step 701 andproceeds to step 702. The BS selects an optimal UL Tx/Rx beam byperforming a UL Tx/Rx beam selecting operation for the UE periodicallyor aperiodically based on the received UL reference signal in step 702and proceeds to step 703.

In step 703, the BS determines whether there is the possibility of theoccurrence of the Tx/Rx beam mismatch between the selected optimal ULTx/Rx beam and a UL Tx/Rx beam actually used for transmittinginformation on the optimal UL Tx/Rx beam. For example, as a result ofthe Tx/Rx beam selecting operation, if an optimal UL Tx/Rx beam having acapability equal to or larger than a particular threshold, for example,threshold 1 is different from a previously selected optimal UL Tx/Rxbeam and the previously selected optimal UL Tx/Rx beam has a capabilityequal to or smaller than a particular threshold, for example, threshold2, the BS determines that a rapid change has occurred in a UL channelenvironment and determines that there is the possibility of theoccurrence of the UL Tx/Rx beam mismatch. The capability of the optimalUL Tx/Rx beam can be measured by a Received Signal Strength Indication(RSSI), a Signal to Interference-plus-Noise Ratio (SINR) or the like.Further, although it has been described as an example that the BSdetermines that there is the possibility of the occurrence of the ULTx/Rx beam mismatch, the BS can also determine that there is apossibility of the occurrence of the DL Tx/Rx beam mismatch by thereciprocity.

Further, if a frequency with which the optimal UL Tx/Rx beam is changedper second is equal to or larger than a particular value, for example, Kor a movement speed of the UE is equal to or larger than a particularvalue, for example, v (km/h), the BS determines that there is a possibleof the occurrence of the DL Tx/Rx beam mismatch. The movement speed ofthe UE can be measured based on a positioning system such as a GlobalPositioning System (GPS) or based on a channel state change between theBS and the UE or a number of handovers per hour.

When the BS determines that there is the possibility of the occurrenceof the Tx/Rx beam mismatch in step 703, the BS performs the proactiveprotection operation for the DL in step 704. That is, the BS increases adiversity effect by widening a width of the DL Tx/Rx beam or increasinga number of Tx/Rx beams to prevent the Tx/Rx beam mismatch in advance.Alternatively, the BS reduces a period of the Tx/Rx beam selectingoperation for selecting the optimal UL Tx/Rx beam or reduces atransmission period of the DL reference signal to prevent the Tx/Rx beammismatch in advance.

Meanwhile, when the BS determines that there is no possibility of theoccurrence of the Tx/Rx beam mismatch in step 703, the BS ends theoperation being currently performed.

FIG. 8 is a flowchart illustrating an example in which the BS determinesa possibility of the occurrence of the Tx/Rx beam mismatch and performsthe reactive compensation operation in the beamforming system accordingto an embodiment of the present disclosure.

Referring to FIG. 8, it is assumed that the BS determines thepossibility of the occurrence of the Tx/Rx beam mismatch in a particularsub-frame n.

The BS receives a UL reference signal and a control signal from the UEin step 801 and proceeds to step 802. The BS selects an optimal UL Tx/Rxbeam by performing a UL Tx/Rx beam selecting operation for the UEperiodically or aperiodically based on the received UL reference signaland control signal in step 802 and proceeds to step 803.

In step 803, the BS determines whether the Tx/Rx beam mismatch occursbetween the selected optimal UL Tx/Rx beam and a UL Tx/Rx beam actuallyused for transmitting information on the optimal UL Tx/Rx beam. Forexample, if the selected optimal UL Tx/Rx beam has a capability of aparticular threshold, for example, a capability equal to or larger thanthreshold 3 and the BS has not received Channel Status Information (CSI)measured and reported for the DL channel by the UE or optimal Tx/Rx beaminformation selected for the DL channel by the UE for a particular time,the BS determines that the UL Tx/Rx beam mismatch occurs. Further, ifthe selected optimal UL Tx/Rx beam has a capability equal to or largerthan threshold 3 and the BS has not continuously received anACKnowledgement (ACK) message of a control signal or data transmitted tothe UE by a predetermined number of times or more, the BS determinesthat the UL Tx/Rx beam mismatch occurs. The capability of the optimal ULTx/Rx beam can be measured by an RSSI, an SINR or the like. Further,although it has been described as an example that the BS determines thatthe UL Tx/Rx beam mismatch occurs, the BS can also determine that the DLTx/Rx beam mismatch occurs by the reciprocity.

When the BS determines that the Tx/Rx beam mismatch occurs in step 803,the BS performs the reactive compensation operation for the DL in step804. The reactive compensation operation will be described in moredetail with reference to FIGS. 9 and 10 described later.

Meanwhile, when the BS determines that the Tx/Rx beam mismatch does notoccurred in step 803, the BS ends the operation being currentlyperformed.

FIG. 9 is a flowchart illustrating an example in which the BS performsthe reactive compensation operation in the beamforming system accordingto an embodiment of the present disclosure.

Referring to FIG. 9, the description of the reactive compensationoperation described below corresponds to a more detailed description ofstep 804 of FIG. 8 and the reactive compensation operation can refer toa reactive compensation operation in a case where the BS determines thatthe Tx/Rx beam mismatch occurs in particular sub-frame n.

Based on an assumption of the reciprocity between the UL and the DL, theBS selects a new DL Tx/Rx beam based on UL Tx/Rx beam informationpre-received from the UE in step 901 and proceeds to step 902. Forexample, the BS can select a DL Tx/Rx beam corresponding to a Tx/Rx beamhaving a most excellent reception capability among UL Tx/Rx beamsreceived from the UE.

The BS transmits compensation information through a scheduling channelor a control channel by using the selected DL Tx/Rx beam in step 902 andproceeds to step 903. The compensation information includes anidentifier of the UE and an optimal UL Tx/Rx beam index.

In step 903, the BS determines whether an ACK message of thecompensation information transmitted in step 902 is received from theUE. If the ACK message is received, the BS proceeds to step 906 tocomplete the reactive compensation operation being performed.

Meanwhile, if the ACK message of the compensation informationtransmitted in step 902 is not received from the UE in step 903, the BSproceeds to step 904. The BS determines whether the compensationinformation is transmitted in all available transmission beam directionsin step 904. When the compensation information is transmitted in allavailable transmission beam directions, the BS ends a communicationconnection process with the UE in step 905. Thereafter, the BS ends thereactive compensation operation in step 907.

However, when the compensation information cannot be transmitted in allavailable transmission beam directions in step 904, the BS proceeds tostep 901 to select a new DL Tx/Rx beam which has not been previouslyselected and re-performs steps 902 and 903.

FIG. 10 is a flowchart illustrating an example in which the BS performsthe reactive compensation operation in the beamforming system accordingto another embodiment of the present disclosure.

Referring to FIG. 10, the description of the reactive compensationoperation described below corresponds to a more detailed description ofstep 804 of FIG. 8 and the reactive compensation operation can refer toa reactive compensation operation in a case where the BS determines thatthe Tx/Rx beam mismatch occurs in particular sub-frame n.

The BS configures an identifier of the UE, information derived from theidentifier of the UE, or information related to the identifier of the UEin a primary BCH region of the DL sub-frame in step 1001 and proceeds tostep 1002. For example, the BS sets a bit corresponding to theidentifier of the UE as “1” among bits included in a bitmap includingthe primary BCH region. The BS transmits a primary BCH signal includingthe configured bitmap to the UE in step 1002 and proceeds to step 1003.

The BS configures compensation information in a secondary BCH region ofthe DL sub-frame in step 1003 and proceeds to step 1004. For example,the BS configures more detailed information indicating the identifier ofthe UE and an index of the optimal UL Tx/Rx beam in the secondary BCHregion. The BS transmits a secondary BCH signal including the moredetailed information indicating the identifier of the UE and the indexof the optimal UL Tx/Rx beam to the UE in step 1004 and proceeds to step1005.

In step 1005, the BS determines whether a response message of thecompensation information transmitted through the secondary BCH signal isreceived from the UE. The response message can be, for example, an ACKmessage of the transmitted compensation information or a messageincluding information on the optimal DL Tx/Rx beam. If the responsemessage is received in step 1005, the BS proceeds to step 1008 tocomplete the reactive compensation operation being performed.

Meanwhile, if the response message is not received from the UE 1005, theBS proceeds to step 1006. The BS determines whether a number of times bywhich the compensation information is transmitted is smaller than apreset maximum retransmission number (MAX ReTX) in step 1006. If thenumber of times by which the compensation information is transmitted issmaller than MAX_RxTX, the BS proceeds to step 1001 and re-performssteps 1001 to 1004. However, when the number of times by which thecompensation information is transmitted is equal to or larger thanMAX_RxTX in step 1006, the BS proceeds to step 1007 to end thecommunication connection process with the UE. Thereafter, the BS endsthe reactive compensation operation in step 1009.

FIG. 11 is a flowchart illustrating an example in which the UEdetermines a possibility of the occurrence of the Tx/Rx beam mismatchand performs the proactive protection operation in the beamformingsystem according to an embodiment of the present disclosure.

Referring to FIG. 11, it is assumed that the UE determines thepossibility of the occurrence of the Tx/Rx beam mismatch in particularsub-frame n.

The UE receives a DL reference signal from the BS in step 1101 andproceeds to step 1102. The UE selects an optimal DL Tx/Rx beam byperforming a DL Tx/Rx beam selecting operation periodically oraperiodically based on the received DL reference signal in step 1102 andproceed to step 1103.

In step 1103, the UE determines whether there is the possibility of theoccurrence of the Tx/Rx beam mismatch between the selected optimal DLTx/Rx beam and a DL Tx/Rx beam actually used for transmittinginformation on the optimal DL Tx/Rx beam. For example, as a result ofthe Tx/Rx beam selecting operation, if an optimal DL Tx/Rx beam having acapability equal to or larger than a particular threshold, for example,threshold 4 is different from a previously selected optimal DL Tx/Rxbeam and the previously selected optimal DL Tx/Rx beam has a capabilityequal to or smaller than a particular threshold, for example, threshold5, the UE determines that a rapid change has occurred in a DL channelenvironment and determines that there is the possibility of theoccurrence of the DL Tx/Rx beam mismatch. The capability of the optimalDL Tx/Rx beam can be measured by an RSSI, an SINR or the like. Further,although it has been described as an example that the UE determines thatthere is the possibility of the occurrence of the DL Tx/Rx beammismatch, the UE can also determine that there is a possibility of theoccurrence of the UL Tx/Rx beam mismatch by the reciprocity.

Further, when a frequency with which the optimal DL Tx/Rx beam ischanged per second is equal to or larger than a particular value, forexample, K or a movement speed of the UE is equal to or larger than aparticular value, for example, v (km/h), the UE determines that there isa possibility of the occurrence of the DL Tx/Rx beam mismatch. Themovement speed of the UE can be measured based on a positioning systemsuch as a Global Positioning System (GPS) or based on a channel statechange between the BS and the UE or a number of handovers per hour.

If the UE determines that there is the possibility of the occurrence ofthe Tx/Rx beam mismatch in step 1103, the UE performs the proactiveprotection operation for the UL in step 1104. That is, the UE increasesa diversity effect by widening a width of the UL Tx/Rx beam orincreasing a number of Tx/Rx beams to prevent the Tx/Rx beam mismatch inadvance. Alternatively, the UE reduces a period of the Tx/Rx beamselecting operation for selecting the optimal DL Tx/Rx beam or reduces atransmission period of the UL reference signal to prevent the Tx/Rx beammismatch in advance.

Meanwhile, when the UE determines that there is no possibility of theoccurrence of the Tx/Rx beam mismatch in step 1103, the UE ends theoperation being currently performed.

FIG. 12 is a flowchart illustrating an example in which the UEdetermines a possibility of the occurrence of the Tx/Rx beam mismatchand performs the reactive compensation operation in the beamformingsystem according to an embodiment of the present disclosure.

Referring to FIG. 12, it is assumed that the UE determines thepossibility of the occurrence of the Tx/Rx beam mismatch in a particularsub-frame n.

The UE receives a DL reference signal and a control signal from the BSin step 1201 and proceeds to step 1202. The UE selects an optimal DLTx/Rx beam by performing a DL Tx/Rx beam selecting operationperiodically or aperiodically based on the received DL reference signalor control signal in step 1202 and proceed to step 1203.

In step 1203, the UE determines whether the Tx/Rx beam mismatch occursbetween the selected optimal DL Tx/Rx beam and a DL Tx/Rx beam actuallyused for transmitting information on the optimal DL Tx/Rx beam. Forexample, when the selected optimal DL Tx/Rx beam has a capability equalto or larger than particular threshold, for example, threshold 6 and theUE has not received optimal Tx/Rx beam information selected for the ULchannel by the BS for a particular time, the UE determines that the DLTx/Rx beam mismatch occurs. Further, if the selected optimal DL Tx/Rxbeam has a capability equal to or larger than threshold 6 and the UE hasnot continuously received an ACK message of a control signal or datatransmitted to the BS by a predetermined number of times or more, the UEdetermines that the DL Tx/Rx beam mismatch occurs. The capability of theoptimal DL Tx/Rx beam can be measured by an RSSI, an SINR or the like.Further, although it has been described as an example that the UEdetermines that the DL Tx/Rx beam mismatch occurs, the UE can alsodetermine that the UL Tx/Rx beam mismatch occurs by the reciprocity.

When the UE determines that the Tx/Rx beam mismatch occurs in step 1203,the UE performs the reactive compensation operation for the UL in step1204. The reactive compensation operation will be described in moredetail with reference to FIGS. 13 and 14 described later.

Meanwhile, if the UE determines that the Tx/Rx beam mismatch does notoccurred in step 1203, the UE ends the operation being currentlyperformed.

FIG. 13 is a flowchart illustrating an example in which the UE performsthe reactive compensation operation in the beamforming system accordingto an embodiment of the present disclosure.

Referring to FIG. 13, the description of the reactive compensationoperation described below corresponds to a more detailed description ofstep 1204 of FIG. 12 and the reactive compensation operation can referto a reactive compensation operation in a case where the UE determinesthat the Tx/Rx beam mismatch occurs in particular sub-frame n.

Based on an assumption of the reciprocity between the UL and the DL, theUE selects a new UL Tx/Rx beam based on DL Tx/Rx beam informationpre-received from the BS in step 1301 and proceeds to step 1302. Forexample, the UE can select a UL Tx/Rx beam corresponding to a Tx/Rx beamhaving a most excellent reception capability among DL Tx/Rx beamsreceived from the BS.

The UE transmits compensation information through a scheduling channelor a control channel by using the selected UL Tx/Rx beam in step 1302and proceeds to step 1303. The compensation information includes anidentifier of the UE and an optimal DL Tx/Rx beam index.

In step 1303, the UE determines whether an ACK message of thecompensation information transmitted in step 1302 is received from theBS. When the ACK message is received, the UE proceeds to step 1306 toselect the reactive compensation operation being performed.

Meanwhile, when the ACK message of the compensation informationtransmitted in step 1303 is not received from the BS in step 1302, theUE proceeds to step 1304. The UE determines whether the compensationinformation is transmitted in all available transmission beam directionsin step 1304. If the compensation information is transmitted in allavailable transmission beam directions, the UE ends a communicationconnection process with the BS in step 1305. Thereafter, the UE ends thereactive compensation operation in step 1307.

However, when the compensation information cannot be transmitted in allavailable transmission beam directions in step 1304, the UE proceeds tostep 1301 to select a new UL Tx/Rx beam which has not been previouslyselected and re-performs steps 1302 and 1303.

FIG. 14 is a flowchart illustrating a process in which the UE receivessystem information in the beamforming system according to an embodimentof the present disclosure.

Referring to FIG. 14, the description will be made based on anassumption that the BS configures compensation information in primaryand secondary BCH regions of the DL sub-frame and transmits thecompensation information. Further, a process in the UE receives thecompensation information configured and transmitted by the BS as systeminformation will be described thereafter.

The UE receives a primary BCH signal of the DL sub-frame transmittedfrom the BS in step 1401 and proceeds to step 1402. The UE determineswhether the received primary BCH signal includes bitmap information inwhich information related to the UE is configured in step 1402. When theprimary BCH signal includes the bitmap information, the UE proceeds tostep 1403.

In step 1403, the UE determines whether a bit corresponding to anidentifier of the UE is set as “1” among bits included in the bitmapincluding the primary BCH signal. When the bit corresponding to theidentifier of the UE among the bits included in the bitmap is set as“1”, the UE receives a secondary BCH signal of the DL sub-frametransmitted from the BS in step 1404. Thereafter, the UE determineswhether compensation information included in the received secondary BCHsignal includes the identifier of the UE in step 1405. If thecompensation information includes the identifier of the UE, the UEproceeds to step 1406. In step 1406, the UE configures an UL Tx/Rx beamindicated by information on an optimal UL Tx/Rx beam included in thesecondary BCH signal as a UL Tx/Rx beam to be used for actualtransmission and transmits a response message of the compensationinformation to the BS. The response message can be, for example, an ACKmessage of the compensation information or a message includinginformation on the optimal DL Tx/Rx beam. Thereafter, the UE receivesSystem Information (SI) included in the DL sub-frame in step 1407.

Meanwhile, when the received primary BCH signal does not include thebitmap information in step 1402, when the bit corresponding to theidentifier of the UE among the bits included in the bitmap is not set as“1” in step 1403, and when the compensation information included in thereceived secondary BCH signal does not include the identifier of the UEin step 1405, the UE proceeds to step 1407 to receive the SI included inthe DL sub-frame transmitted from the BS.

FIG. 15 is a block diagram illustrating a structure of a BS apparatusthat provides an optimal Tx/Rx beam to a UE by solving the Tx/Rx beammismatch problem in the beamforming system according to an embodiment ofthe present disclosure.

Referring to FIG. 15, a BS 1500 includes a transmitter 1502, a receiver1504, and a controller 1506.

First, an operation in which the BS 1500 provides the optimal Tx/Rx beamthrough a proactive protection scheme will be described below.

The receiver of the BS 1500 receives a UL reference signal from the UEand the controller 1506 selects an optimal UL Tx/Rx beam by performing aUL Tx/Rx beam selecting operation for the UE periodically oraperiodically based on the UL reference signal received through thereceiver 1504.

The controller 1506 of the BS 1500 determines whether there is apossibility of the occurrence of the Tx/Rx beam mismatch between theselected optimal UL Tx/Rx beam and a UL Tx/Rx beam actually used fortransmitting information on the optimal UL Tx/Rx beam. That is, as aresult of the Tx/Rx beam selecting operation, when an optimal UL Tx/Rxbeam having a capability equal to or higher than threshold 1 isdifferent from a previously selected optimal UL Tx/Rx beam and thepreviously selected optimal UL Tx/Rx beam has a capability equal to orsmaller than threshold 2, the controller 1506 determines that a rapidchange has occurred in a UL channel environment and determines thatthere is the possibility of the occurrence of the UL Tx/Rx beammismatch. The capability of the optimal UL Tx/Rx beam can be measured byan RSSI, an SINR or the like. Further, although it has been described asan example that the controller 1506 of the BS 1500 determines that thereis the possibility of the occurrence of the UL Tx/Rx beam mismatch, thecontroller 1506 can also determine that there is a possibility of theoccurrence of the DL Tx/Rx beam mismatch by the reciprocity.

Further, when a frequency with which the optimal UL Tx/Rx beam ischanged per second is equal to or larger than a preset value K or amovement speed of the UE is equal to or larger than a preset speed v(km/h), the controller 1506 of the BS 1500 determines that there is thepossibility of the occurrence of the DL Tx/Rx beam mismatch. Thereafter,when the controller 1506 determines that there is the possibility of theoccurrence of the Tx/Rx beam mismatch, the controller 1506 performs theproactive protection operation for the DL. That is, the controller 1506of the BS 1500 increases a diversity effect by widening a width of theDL Tx/Rx beam or increasing a number of Tx/Rx beams to prevent the Tx/Rxbeam mismatch in advance. Alternatively, the controller 1506 of the BS1500 reduces a period of the Tx/Rx beam selecting operation forselecting the optimal UL Tx/Rx beam or reduces a transmission period ofthe DL reference signal to prevent the Tx/Rx beam mismatch in advance.

Next, an operation in which the BS 1500 provides the optimal Tx/Rx beamthrough a reactive compensation scheme will be described below.

The receiver 1504 of the BS 1500 receives a UL reference signal and acontrol signal from the UE and the controller 1506 selects an optimal ULTx/Rx beam by performing a UL Tx/Rx beam selecting operation for the UEperiodically or aperiodically based on the UL reference signal andcontrol signal received through the receiver 1504.

The controller 1506 of the BS 1500 determines whether there the Tx/Rxbeam mismatch occurs between the selected optimal UL Tx/Rx beam and a ULTx/Rx beam actually used for transmitting information on the optimal ULTx/Rx beam. That is, when the selected optimal UL Tx/Rx beam has acapability equal to or larger than threshold 3 and Channel StatusInformation (CSI) measured and reported for the DL channel by the UE oroptimal Tx/Rx beam information selected for the UL channel by the UE hasnot been received for a particular time, the controller 1506 determinesthat the UL Tx/Rx beam mismatch occurs. Further, when the selectedoptimal UL Tx/Rx beam has a capability equal to or larger than threshold3 and the an ACK message of a control signal or data transmitted to theUE has not been continuously received by a predetermined number of timesor more, the controller 1506 determines that the UL Tx/Rx beam mismatchoccurs. The capability of the optimal UL Tx/Rx beam can be measured byan RSSI, an SINR or the like. Further, although it has been described asan example that the controller 1506 of the BS 1500 determines that theUL Tx/Rx beam mismatch occurs, the controller 1506 can also determinethat the DL Tx/Rx beam mismatch occurs by the reciprocity.

When the controller 1506 of the BS 1500 determines that the Tx/Rx beammismatch occurs, the controller 1506 performs a reactive compensationoperation for the DL. That is, based on an assumption of the reciprocitybetween the UL and the DL, the controller 1506 selects a new DL Tx/Rxbeam based on UL Tx/Rx beam information pre-received from the UE throughthe receiver 1504. The new DL Tx/Rx beam can be a DL Tx/Rx beamcorresponding to a Tx/Rx beam having a most excellent capability amongUL Tx/Rx beams received from the UE.

The transmitter 1502 of the BS 1500 transmits compensation informationthrough a scheduling channel or a control channel by using the selectedDL Tx/Rx beam. The compensation information includes an identifier ofthe UE and an optimal UL Tx/Rx beam index.

The receiver 1504 of the BS 1500 determines whether an ACK message ofthe compensation information transmitted through the transmitter 1502 isreceived from the UE. When the ACK message is received, the BS 1500completes the reactive compensation operation being performed. However,when the ACK message of the compensation information transmitted throughtransmitter 1502 is not received, the receiver 1504 of the BS 1500determines whether the transmitter 1502 transmits the compensationinformation in all available transmission beam directions. When thecompensation information is transmitted in all available transmissionbeam directions, a communication connection process with the UE and thereactive compensation operation end. However, when the transmitter 1502has not transmitted the compensation information in all availabletransmission beam directions, the BS 1500 selects a new DL Tx/Rx beamwhich has been previously selected, through the controller 1506, and thetransmitter 1502 re-transmits the compensation information by using theselected new DL Tx/Rx beam.

Meanwhile, when re-transmitting the compensation information, thetransmitter 1502 of the BS 1500 configures an identifier of the UE,information derived from the identifier of the UE, or informationrelated to the identifier of the UE in a primary BCH region of the DLsub-frame. That is, the transmitter 1502 configures a bit correspondingto the identifier of the UE among bits included in a bitmap as “1”.Further, the transmitter 1502 configures more detailed informationindicating the identifier of the UE and an index of the optimal Tx/Rxbeam in a secondary BCH region of the DL sub-frame. Thereafter, thetransmitter transmits the DL sub-frame including the configured primaryand secondary BCH regions to the UE. Next, the controller 1506 of the BS1500 determines whether a response message of the compensationinformation configured and transmitted in the secondary BCH region isreceived, from the UE. The response message can be, for example, an ACKmessage of the transmitted compensation information or a messageincluding information on the optimal DL Tx/Rx beam.

FIG. 16 is a block diagram illustrating a structure of a UE apparatusthat provides an optimal Tx/Rx beam to a BS by solving the Tx/Rx beammismatch problem in the beamforming system according to an embodiment ofthe present disclosure.

Referring to FIG. 16, a UE 1600 includes a transmitter 1602, a receiver1604, and a controller 1606.

First, an operation in which the UE 1600 provides the optimal Tx/Rx beamthrough a proactive protection scheme will be described below.

The receiver 1604 of the UE 1600 receives a DL reference signal from theBS and the controller 1606 selects an optimal DL Tx/Rx beam byperforming a DL Tx/Rx beam selecting operation periodically oraperiodically based on the DL reference signal received through thereceiver 1604.

The controller 1606 of the UE 1600 determines whether there is apossibility of the occurrence of the Tx/Rx beam mismatch between theselected optimal DL Tx/Rx beam and a DL Tx/Rx beam actually used fortransmitting information on the optimal DL Tx/Rx beam. That is, as aresult of the Tx/Rx beam selecting operation, when an optimal DL Tx/Rxbeam having a capability equal to or larger than threshold 4 isdifferent from a previously selected optimal DL Tx/Rx beam and thepreviously selected optimal DL Tx/Rx beam has a capability equal to orsmaller than threshold 5, the controller 1606 determines that a rapidchange has occurred in a DL channel environment and determines thatthere is the possibility of the occurrence of the DL Tx/Rx beammismatch. The capability of the optimal DL Tx/Rx beam can be measured byan RSSI, an SINR or the like. Further, although it has been described asan example that the controller 1606 of the UE 1600 determines that thereis the possibility of the occurrence of the DL Tx/Rx beam mismatch, thecontroller 1606 can also determine that there is a possibility of theoccurrence of the UL Tx/Rx beam mismatch by the reciprocity.

Further, when a frequency with which the optimal DL Tx/Rx beam ischanged per second is equal to or larger than a preset value K or amovement speed of the UE is equal to or larger than a preset speed v(km/h), the controller 1606 of the UE 1600 determines that there is thepossibility of the occurrence of the DL Tx/Rx beam mismatch. Thereafter,when the controller 1606 determines that there is the possibility of theoccurrence of the Tx/Rx beam mismatch, the controller 1606 performs theproactive protection operation for the UL. That is, the controller 1606of the UE 1600 increases a diversity effect by widening a width of theUL Tx/Rx beam or increasing a number of Tx/Rx beams to prevent the Tx/Rxbeam mismatch in advance. Alternatively, the controller 1606 of the UE1600 reduces a period of the Tx/Rx beam selecting operation forselecting the optimal DL Tx/Rx beam or reduces a transmission period ofthe UL reference signal to prevent the Tx/Rx beam mismatch in advance.

Next, an operation in which the UE 1600 provides the optimal Tx/Rx beamthrough a reactive compensation scheme will be described below.

The receiver 1604 of the UE 1600 receives a DL reference signal and acontrol signal from the BS and the controller 1606 selects an optimal DLTx/Rx beam by performing a DL Tx/Rx beam selecting operationperiodically or aperiodically based on the DL reference signal orcontrol signal received through the receiver 1604.

The controller 1606 of the UE 1600 determines whether the Tx/Rx beammismatch occurs between the selected optimal DL Tx/Rx beam and a DLTx/Rx beam actually used for transmitting information on the optimal DLTx/Rx beam. That is, when the selected optimal DL Tx/Rx beam has acapability equal to or larger than threshold 6 and optimal Tx/Rx beaminformation selected for the UL channel by the BS has not been receivedfor a particular time, the controller 1606 determines that the DL Tx/Rxbeam mismatch occurs. Further, when the selected optimal DL Tx/Rx beamhas a capability equal to or larger than threshold 6 and an ACK messageof a control signal or data transmitted to the BS has not beencontinuously received by a predetermined number of times or more, thecontroller 1606 determines that the DL Tx/Rx beam mismatch occurs. Thecapability of the optimal DL Tx/Rx beam can be measured by an RSSI, anSINR or the like. Further, although it has been described as an examplethat the controller 1606 of the UE 1600 determines that the DL Tx/Rxbeam mismatch occurs, the controller 1606 can also determine that the ULTx/Rx beam mismatch occurs by the reciprocity.

When the controller 1606 of the UE 1600 determines that the Tx/Rx beammismatch occurs, the controller 1606 performs a reactive compensationoperation for the UL. That is, based on an assumption of the reciprocitybetween the UL and the DL, the controller 1606 selects a new UL Tx/Rxbeam based on DL Tx/Rx beam information pre-received from the BS throughthe receiver 1604. The new UL Tx/Rx beam can be a UL Tx/Rx beamcorresponding to a Tx/Rx beam having a most excellent receptioncapability among DL Tx/Rx beams received from the BS.

The transmitter 1602 of the UE 1600 transmits compensation informationthrough a scheduling channel or a control channel by using the selectedUL Tx/Rx beam in step. The compensation information includes anidentifier of the UE and an optimal DL Tx/Rx beam index.

The receiver 1604 of the UE 1600 determines whether an ACK message ofthe compensation information transmitted through transmitter 1602 isreceived from the BS. When the ACK message is received, the UE 1600completes the reactive compensation operation being performed. However,when the ACK message of the compensation information transmitted throughtransmitter 1602 is not received, the receiver 1604 of the UE 1600determines whether the transmitter 1602 transmits the compensationinformation in all available transmission beam directions. When thecompensation information is transmitted in all available transmissionbeam directions, a communication connection process with the BS and thereactive compensation operation end. However, when the transmitter 1602has not transmitted the compensation information in all availabletransmission beam directions, the UE 1600 selects a new UL Tx/Rx beamwhich has been previously selected, through the controller 1606, and thetransmitter 1602 re-transmits the compensation information by using theselected new UL Tx/Rx beam.

Meanwhile, the receiver 1604 of the UE 1600 receives the compensationinformation configured in primary and secondary BCH regions of the DLsub-frame and transmitted, as system information, and determines whetherbitmap information in which information related to the UE is configuredis included in the primary BCH region. When the bitmap information isincluded in the primary BCH region, the controller 1606 determines a bitcorresponding to an identifier of the UE among bits included in thebitmap. When the bit corresponding to the identifier of the UE is “1”,the controller 1606 determines whether compensation information includedin the secondary BCH region includes the identifier of the UE. When thecompensation information includes the identifier of the UE, thecontroller 1606 configures a UL Tx/Rx beam indicated by optimal Tx/Rxbeam information configured in the secondary BCH region as a UL Tx/Rxbeam to be used for actual transmission/reception. Thereafter, thetransmitter 1602 of the UE 1600 transmits a response message of thecompensation information to the BS. The response message can be, forexample, an ACK message of the compensation information or a messageincluding information on the optimal DL Tx/Rx beam.

Although concrete embodiments have been described in the detaileddescription of the present disclosure, the embodiments can be modifiedin various forms without departing from the scope of the presentdisclosure. Therefore, the scope of the present disclosure is notlimited to the embodiments described above, and should be defined by theappended claims and the equivalents thereof.

Further, a method and an apparatus for providing an optimal Tx/Rx beamaccording to an embodiment of the present disclosure can be implementedin the form of hardware, software, or a combination thereof. Any suchsoftware can be stored, for example, in a volatile or non-volatilestorage device such as a ROM, a memory such as a RAM, a memory chip, amemory device, or a memory IC, or a recordable optical or magneticmedium such as a CD, a DVD, a magnetic disk, or a magnetic tape,regardless of its ability to be erased or its ability to be re-recorded.It can be also appreciated that the memory included in the mobileterminal is one example of machine-readable devices suitable for storinga program including instructions that are executed by a processor deviceto thereby implement embodiments of the present disclosure.

Accordingly, the present disclosure includes a program including a codefor implementing the apparatus and method described in the appendedclaims of the specification and a machine (a computer or thelike)-readable storage medium for storing the program. Moreover, such aprogram can be electronically transferred through an arbitrary mediumsuch as a communication signal transferred through a wired or wirelessconnection, and the present disclosure properly includes the equivalentsthereof.

In addition, the apparatus for providing the optimal Tx/Rx beamaccording to the embodiment of the present disclosure can receive aprogram from a program providing apparatus connected to the apparatuswirelessly or through a wire and store the received program. The programproviding apparatus can include a program for instructing to perform apreset content protecting method, a memory for storing informationrequired for the content protecting method, a communication unit forperforming wired or wireless communication with the apparatus forproviding the optimal Tx/Rx beam, and a controller for transmitting thecorresponding program to a transmission/reception device according to arequest of the apparatus for providing the optimal Tx/Rx beam orautomatically.

Although the present disclosure has been described with an exemplaryembodiment, various changes and modifications may be suggested to oneskilled in the art. It is intended that the present disclosure encompasssuch changes and modifications as fall within the scope of the appendedclaims.

What is claimed is:
 1. A method of providing an optimal transmission orreception (Tx/Rx) beam in a beamforming system, the method comprising:receiving a reference signal and a control signal; selecting an optimalTx/Rx beam that guarantees an optimal channel environment based on thereceived reference signal and control signal; determining whether aTx/Rx beam mismatch occurs between the selected optimal Tx/Rx beam andan Tx/Rx beam used for transmitting information related to the selectedoptimal Tx/Rx beam; if the Tx/Rx beam mismatch occurs, selecting a newTx/Rx beam based on pre-received Tx/Rx beam information; andtransmitting compensation information including at least one ofinformation related to a user equipment (UE) and information related tothe optimal Tx/Rx beam through the new Tx/Rx beam.
 2. The method ofclaim 1, wherein the determining whether the Tx/Rx beam mismatch occurscomprises: determining whether the optimal Tx/Rx beam has a capabilityequal to or larger than a first threshold; if the optimal Tx/Rx beam hasthe capability equal to or larger than the first threshold, determiningwhether response messages of pre-transmitted control signals or datahave been received more than a predetermined number of times or more;and if the response messages have not been received more that thepredetermined number of times or more, determining that the Tx/Rx beammismatch occurs.
 3. The method of claim 1, wherein the determiningwhether the Tx/Rx beam mismatch occurs comprises: determining whetherthe optimal Tx/Rx beam has a capability equal to or larger than a firstthreshold; if the optimal Tx/Rx beam has the capability equal to orlarger than the first threshold, determining whether channel statusinformation measured and reported by the UE or information related to anoptimal Tx/Rx beam selected by the UE has been received within apredetermined time; and if the channel status information or theinformation on the optimal Tx/Rx beam selected by the UE has not beenreceived within the predetermined time, determining that the Tx/Rx beammismatch occurs.
 4. The method of claim 1, wherein the determiningwhether the Tx/Rx beam mismatch occurs comprises: determining whetherthe optimal Tx/Rx beam has a capability equal to or larger than a firstthreshold; if the optimal Tx/Rx beam has the capability equal to orlarger than the first threshold, determining whether information on anoptimal Tx/Rx beam selected by a base station (BS) has been receivedwithin a predetermined time; and if the information related to theoptimal Tx/Rx beam selected by the BS has not been received within thepredetermined time, determining that the Tx/Rx beam mismatch occurs. 5.The method of claim 1, wherein the transmitting the compensationinformation comprises: configuring at least one of information relatedto the UE and information related to the optimal Tx/Rx beam in abroadcasting channel (BCH) region and transmitting the configuredinformation in all beam directions.
 6. The method of claim 1, whereinthe selecting the new Tx/Rx beam comprises selecting a new DL Tx/Rx beambased on a pre-received uplink (UL) Tx/Rx beam or selecting a new ULTx/Rx beam based on a pre-received downlink (DL) Tx/Rx beam based on thereciprocality between UL and DL.
 7. The method of claim 1, wherein thetransmitting the compensation information comprises: configuring anidentifier of the UE or information derived from the identifier of theUE in a primary broadcasting channel (BCH) region of a downlink (DL)sub-frame; configuring information related to the identifier of the UEand information related to the optimal Tx/Rx beam in a secondary BCHregion of the DL sub-frame; and transmitting the DL sub-frame includingthe primary and secondary BCH regions.
 8. The method of claim 1, furthercomprising: receiving a downlink (DL) sub-frame including primary andsecondary broadcasting channel (BCH) regions; if bitmap information isincluded in the primary BCH region, determining a bit related to anidentifier of the UE among bits included in a bitmap; and if the bitrelated to the identifier of the UE is “1”, setting a Tx/Rx beamindicated by information on the optimal Tx/Rx beam included in thesecondary BCH region as a Tx/Rx beam to be used for actual transmissionor reception.
 9. The method of claim 1, further comprising: determiningwhether the optimal Tx/Rx beam having a capability equal to or largerthan a first threshold is identical to a previously selected optimalTx/Rx beam; if the optimal Tx/Rx beam is not identical to the previouslyselected optimal Tx/Rx beam, determining whether the previously selectedTx/Rx beam has a capability equal to or smaller than a second threshold;and if the previously selected Tx/Rx beam has the capability equal to orsmaller than the second threshold, determining that there is apossibility of an occurrence of the Tx/Rx beam mismatch.
 10. The methodof claim 1, further comprising: determining whether a frequency withwhich the optimal Tx/Rx beam is changed per second is equal to or largerthan a preset value; and if the frequency with which the optimal Tx/Rxbeam is changed per second is equal to or larger than the preset value,determining that there is a possibility of the occurrence of the Tx/Rxbeam mismatch.
 11. The method of claim 1, further comprising:determining whether a movement speed of a user equipment (UE) is equalto or faster than a preset speed; and if the movement speed of the UE isequal to or faster than the preset speed, determining that there is apossibility of the occurrence of the Tx/Rx beam mismatch.
 12. Anapparatus for providing an optimal transmission or reception (Tx/Rx)beam in a beamforming system, the apparatus comprising: a receiverconfigured to receive a reference signal and a control signal; acontroller configured to: select an optimal Tx/Rx beam that guaranteesan optimal channel environment based on the received reference signaland control signal; determine whether a Tx/Rx beam mismatch occursbetween the selected optimal Tx/Rx beam and a Tx/Rx beam used fortransmitting information on the selected optimal Tx/Rx beam; and if theTx/Rx beam mismatch occurs, select a new Tx/Rx beam based onpre-received Tx/Rx beam information; and a transmitter configured totransmit compensation information including at least one of informationrelated to a user equipment (UE) and information related to the optimalTx/Rx beam through the new Tx/Rx beam.
 13. The apparatus of claim 12,wherein the controller is configured to: determine whether the optimalTx/Rx beam has a capability equal to or larger than a first threshold;if the optimal Tx/Rx beam has the capability equal to or larger than thefirst threshold, determine whether response messages of pre-transmittedcontrol signals or data have been received more than a predeterminednumber of times or more; and if the response messages have not beenreceived more than the predetermined number of times or more, determinethat the Tx/Rx/bean mismatch occurs.
 14. The apparatus of claim 12,wherein the controller is configured to: determine whether the optimalTx/Rx beam has a capability equal to or larger than a first threshold;if the optimal Tx/Rx beam has the capability equal to or larger than thefirst threshold, determine whether channel status information measuredand reported by the UE or information related to an optimal Tx/Rx beamselected by the UE has been received within a predetermined time; and ifthe channel status information or the information on the optimal Tx/Rxbeam selected by the UE has not received within the predetermined time,determine that the Tx/Rx beam mismatch occurs.
 15. The apparatus ofclaim 12, wherein the controller is configured to: determine whether theoptimal Tx/Rx beam has a capability equal to or larger than a firstthreshold; if the optimal Tx/Rx beam has the capability equal to orlarger than the first threshold, determine whether information on anoptimal Tx/Rx beam selected by a base station (BS) has been receivedwithin a predetermined time; and if the information related to theoptimal Tx/Rx beam selected by the BS has not been received within thepredetermined time, determine that the Tx/Rx beam mismatch occurs. 16.The apparatus of claim 12, wherein the transmitter is configured to:configure at least one of information related to the UE and informationrelated to the optimal Tx/Rx beam in a broadcasting channel (BCH) regionand transmits the configured information in all beam directions.
 17. Theapparatus of claim 12, wherein the controller is configured to: select anew DL Tx/Rx beam based on a pre-received uplink (UL) Tx/Rx beam, or anew UL Tx/Rx beam based on a pre-received downlink (DL) Tx/Rx beam basedon the reciprocality between UL and DL.
 18. The apparatus of claim 12,wherein the transmitter is configured to: configure an identifier of theUE or information derived from the identifier of the UE in a primarybroadcasting channel (BCH) region of a downlink (DL) sub-frame;configure information related to the identifier of the UE andinformation related to the optimal Tx/Rx beam in a secondary BCH regionof the DL sub-frame; and transmit the DL sub-frame including the primaryand secondary BCH regions.
 19. The apparatus of claim 12, wherein: thereceiver is configured to receive a downlink (DL) sub-frame includingprimary and secondary broadcasting channel (BCH) regions; and thecontroller is configured to: if bitmap information is included in theprimary BCH region, determine a bit related to an identifier of the UEamong bits included in a bitmap; and if the bit related to theidentifier of the UE is “1”, set a Tx/Rx beam indicated by informationon the optimal Tx/Rx beam included in the secondary BCH region as aTx/Rx beam to be used for actual transmission or reception.
 20. Theapparatus of claim 12, wherein: the controller is further configured to:determine whether the optimal Tx/Rx beam having a capability equal to orlarger than a first threshold is identical to a previously selectedoptimal Tx/Rx beam; if the optimal Tx/Rx beam is not identical to thepreviously selected optimal Tx/Rx beam, determine whether the previouslyselected Tx/Rx beam has a capability equal to or smaller than a secondthreshold; and if the previously selected Tx/Rx beam has the capabilityequal to or smaller than the second threshold, determine that there is apossibility of an occurrence of the Tx/Rx beam mismatch.